redistribute solar heat in sea water across the Earth; affects Earth's weather and climate

Gyres

Current systems involving return flow of cold water to lower latitudes; mainly occurs in large ocean basins

Upwelling

colder deep water flows up at coastal areas due to wind energy pushing surface water away from land

Bottom currents

cold water from polar areas that flows down to sea floor and toward the equator; cold water is colder the more dense

Saltiness of the Ocean

due to weathering of rocks on land, and transportation of dissolved elements into the sea; saltiness at present level since 3.5 billion years ago

Removal of Salt from Ocean

evaportaion of seawater causes saturation and then precipitation of salt crystals; organisms in the sea also take up dissolved minerals

Return of Salt to the SEA

sediments of the ocean form layers of sedimentary rock that are pushed up into folded mountains, eroded away and transported to the ocean via rivers and streams; subduction may also result in melting of these sediments and chemical return to the ocean via volcanoes